The present invention relates generally to improvements in copying machines and it relates particularly to an improved document hold-down cover for use in a copying apparatus, in which a document to be reproduced is placed on a document supporting glass plate in intimate contact therewith.
In general, the requirements for the prior art document hold-down cover for use in a copying apparatus are such that the document hold-down plate should be made of a material whose surface reflects the light from the illuminating lamp, particularly, in a diffuse manner; thermal deterioration due to the heat from the illuminating lamp should be minimized; the document hold-down surface of the plate should afford sufficient flexibility to accommodate itself to an irregularity of the surface of a document; and the document hold-down surface should be stain resistant and easy to be cleaned, even if it is stained.
The document hold-down means may be generally classified into two types; one type in which a soft polyurethane foam sheet is bonded to the undersurface of a rigid plate, and then a white rubber sheet is bonded to the undersurface of the polyurethane foam sheet, so that the undersurface of the white rubber sheet functions as a document hold-down surface, while one edge of the rigid plate is hinged to the body of the copying apparatus, and the opposite edge of the rigid plate has a grip attached thereto; and the other type in which a laminated rubber plate is used which includes a white rubber sheet providing a document hold-down surface, one edge of the laminated rubber plate being hinged to the body of the copying apparatus, and the other edge of the plate having a grip attached thereto, a manner similar to the first type.
Since the both types of document hold-down devices are hinged to the body of the copying apparatus, there is the need to provide a rotary shaft, bearings, and the like on the copying apparatus or on the document hold-down cover. Particularly, in the case of a document having a considerable thickness, a parallel link mechanism should be provided to absorb or accommodate itself to an excessively thick document. This results in an increase in the number of parts constituting the document hold-down cover means, and hence a complex arrangement which leads to an increased manufacturing cost. Such a complex arrangement of the document hold-down cover means causes difficulty in attaching it to or removing it from the copying apparatus, and as a result, problems often occur. Furthermore, once the white rubber plate is stained or dirtied, the stains or dirt are hard to remove, so that the stains appear in the reproduced copy. Additionally, the document hold-down cover includes a soft urethane foam sheet. Moreover, the thickness of the rubber plate providing a document hold-down surface can not be reduced from viewpoint of ease of manufacture or required strength thereby failing to properly accommodate itself to the irregular surface of a document, with the result that uneven portions of the document appear in the copy black or shaded.
Still further, a document hold-down cover should exceed a predetermined weight, but an increase in the weight of the rubber plate in the latter case leads to an increase in cost. In addition, the document hold-down cover made of a rubber plate of considerable thickness tends to cause shading in the reproduced copy due to the irregular surface of the document.
Furthermore, a supporting member is generally provided for supporting the conventional document hold-down cover, when the cover is opened at an angle of about 120.degree. to the surface of the document supporting glass plate. However, it is undesirable from the viewpoint of handling the document hold-down cover to open it through angles of over 90.degree.. Still further, various kinds of devices such as a spring member and the like are used for urging the document hold-down plate against the document supporting glass plate through the medium of the document, when the document hold-down cover assumes a closed position, thereby posing a further problem in achieving simplicity in the copying apparatus.